1. Field of the Invention
The invention relates to an apparatus for the continuous determination of two physical properties of the constituents of a smokable article from the mechanical properties of a rod of tobacco or filter fibres during the manufacture of said rod, comprising a format finger for compacting the rod to a predetermined diameter.
2. Description of the Prior Art
For the quality control in cigarette manufacture, ever increasing attention is being paid to the hardness of the cigarettes and filters because it can be determined in relatively simple manner from a hardness measurement whether or not a smokable article, for example a cigarette, is adequately filled. And it is precisely the defective filling of smokable articles which is a frequent reason for complaint.
Consequently, in an article from "Beitrage zur Tabakforschung", Volume 4, No. 7, December 1968, a device for testing the hardness of cigarettes is described, in which the diameter change of cigarettes under a specific load is measured after a predetermined time and the hardness derived therefrom. However, this practically static method is suitable only for random checks and therefore cannot be employed for the everyday, continuous monitoring of the hardness of the smokable article during the production and for the corresponding control of the entire production.
In addition, U.S Pat. No. 3,411,513 discloses a method in which a moving, finished tobacco rod sheathed in paper is deformed by an air stream and the associated follow-up of the nozzle is detected. The occurring movement of the nozzle is related to the filling force of the tobacco and thus to the hardness of the cigarette. The obtained information, however, is influenced by diameter fluctuations and the porosity of the cigarette paper; consequently only in a few cases is there an exact correlation with the static measurement of the hardness by the determination of the penetration depth, as known from this article.
Furthermore, various methods are known in which the deformation of the format finger under the influence of the flow of tobacco fibres therealong is detected and thus a continuous measurement signal is obtained which is supposed to be in correlation with the hardness of the finished cigarette. Thus, German Offenlegungsschrift 22 41 774 discloses an apparatus in which a force transducer, generally a strain gauge, is provided which detects the deformation of the support bridge for the format finger. Another variant is known from German Offenlegungsschrift 24 57 141 in which the deflection of the front portion of the two-part format finger under the action of the rod of tobacco fibres is determined. Finally, U.S. Pat. No. 2,667,172 discloses an apparatus which detects at various points the vertical and horizontal forces which the tobacco rod exerts on its guide and in particular on the format finger. Thus, for example, the width of the gap between the front end of the format finger and a transducer is detected, i.e. the deflection of the front end of the format finger.
German patent 32 04 342 discloses an apparatus for measuring the compressibility of tobacco within a tobacco stream transported on a continuously driven conveyor wherein at least two rollers disposed in series in the conveying direction are applied to the tobacco stream; considered in the conveying direction, the downstream roller exerts a greater pressure action on the stream than the upstream roller; associated with the rollers are transducers, for determining the magnitude of the deformations of the tobacco stream produced by the rollers; the outputs of said transducers are connected to an evaluation circuit for forming from said parameters a function providing a measure of the compressibility of the tobacco. Thus, in this manner the compressibility is determined by comparison measurement at two different points along the processing path of the rod at which said rod has different heights or is subjected to different pressure forces.
However, in apparatuses of the type according to U.S. Pat. No. 3,411,513, German Offenlegungsschrift 22 41 774, German Offenlegungsschrift 24 57 141 and U.S. Pat. No. 2,667,172, the result of the measurement correlates linearly with the hardness of the finished cigarette only when the deformation of the format finger is detected at the location where the diameter of the rod of tobacco fibres corresponds substantially to the tobacco diameter of the finished smokable article as is known from German Offenlegungsschrift 33 06 538; although not expressly mentioned therein, this fact is also implemented substantially in the final result for the apparatus according to the German Offenlegungsschrift 24 57 141.
Furthermore, in the quality control of cigarettes the draw resistance of the cigarette is of great importance because from a draw resistance measurement, it is possible to determine in relatively simple manner whether a cigarette permits the desired draw volume. The draw volume of a cigarette in turn is governed firstly by the manner in which the smoker smokes the cigarette and secondly by its draw resistance which is constituted by the draw resistance of the tobacco rod and of the filter.
Thus, to always ensure for the smoker of a given brand cigarette the same draw volume--keeping the subjective parameter, that is the manner in which the smoker smokes the cigarette, constant--the draw resistance must be kept to a fixed value.
To ensure that this constant draw resistance value is maintained individual cigarettes are taken in random checks from the everyday production and their draw resistance determined with a device as described, for example, in the article "The Measurement of Smoking Parameters with the Aid of Parameter Converters", published in "Beitrage zur Tabakforschung", Volume 6, No. 1, July 1971. In this method the cigarette is connected by means of a rubber lip to a smoking machine which, for example, draws a gas flow with constant volume through the cigarette. In accordance with the usual standardization, the constant flow volume at the exit side should be 17.5 cm.sup.3 /sec.
Due to the flow resistance of the cigarette a pressure drop occurs between the entry side and exit side of the gas flow and is referred to as "draw resistance"; it can be measured by a pressure transducer.
Alternatively, it is fundamentally also possible with constant pressure drop to measure the gas volume passing through the cigarette.
These apparatuses are, however, only suitable for carrying out random checks, i.e. cannot be used for the everyday continuous measurement of the draw resistance of all cigarettes, for example those made by a certain cigarette machine, because each cigarette must be inserted into the apparatus and measured individually. These random checks can only be carried out at predetermined intervals of time so that in general it is not possible to react immediately to a detected change of the draw resistance of the cigarette by appropriate regulation of the production cycle.
British Pat. No. 1,588,506 discloses an apparatus for measuring the draw resistance of a rod of filter fibres with which the pressure drop at the rod is detected in a region at which the rod has reached almost its final cross-section. The intention is to detect the pressure drop at a location downstream from the smallest cross-section of the rod of filter material because there the filter fibres have reached their final position and thus can no longer be displaced by the air passing through the rod. The main compression of the rod is by means of a wheel whilst the shaping and subsequent compression is carried out by a format finger which is arranged in the movement direction of the rod downstream from the wheel.
A further aparatus for measuring the draw resistance of a rod of tobacco fibres is disclosed in German Auslegeschrift 11 66 069 and comprises a source for a gas flow passing through the rod and a measuring-value transducer for determining the pressure drop of the gas flow with constant gas volume occurring at the rod or of the gas volume with constant pressure drop passing through the rod. A pump passes the air through the tobacco flow into an enclosed space of constant volume which is formed between a trough through which the format belt draws the tobacco stream and a member opposite said trough, for instance a pressure shoe or a tongue as known per se.
Admittedly, this permits the continuous measurement of the draw resistance of a rod of tobacco fibres; the value determined is also specific for the rod of tobacco fibres so that the draw resistance determined can be used for process control. A disadvantage, however, is that the draw resistance of the rod of tobacco fibres thus determined does not correlate with the draw resistance of the finished cigarette which is a very important product parameter because it is an essential characteristic of a specific cigarette type.